Impact of β-mannanase supplementation on broilers fed low-energy diets: A phase feeding meta-analysis

The presence of β-mannans in poultry feed ingredients and their associated negative effects on nutrient utilization and production performance remain a concern for the poultry industry. Despite efforts to address these effects by exploiting commercial enzymes, like β-mannanase, responses across reported studies remain inconsistent. Hence, this meta-analysis, with a focus on phase feeding, aimed to determine whether β-mannanase supplementation improves growth performance, nutrient digestibility, histomorphology, and immune organ weight in broilers fed low-energy diets. It also explored the source of between-study variation. A literature search from 2004 to August 2024 identified 27 eligible studies. Data from these studies were pooled using Hedges' g to estimate the standardized mean difference (SMD) with 95% confidence intervals. Heterogeneity was addressed through subgroup and meta-regression analyses based on β-mannan source, mannan degrader, β-mannanase dose, trial duration, and broiler strain. The quality of the eligible studies was also assessed using the risk of bias checklists for animal studies (SYRCLE) of the Cochrane Collaboration. The random-effects model's SMD estimates revealed that BWG and FCR are markedly improved by β-mannanase in the starter phase compared to the grower phase. However, the dose effect on FCR is influenced by an interaction with duration, which gradually diminishes as the later phase of grow-out progresses. In addition, β-mannanase improved DM and CP digestibility and increased VH, the VH-to-CD ratio, and innate activation (spleen) to maintain intestinal function and efficient nutrient utilization. However, the enzyme's effects on responses can be influenced by dose, its interaction with trial duration, and, to a lesser extent, by mannan source, degrader type, and the broiler strain. This meta-analysis demonstrates that β‑mannanase supplementation is a reliable strategy for mitigating the antinutritive effects of β‑mannans in broiler diets. Supplementation of the enzyme at 968 g/ton within reduced‑energy, phase‑feeding programs consistently improves growth performance, particularly during the starter phase, while maintaining key physiological indicators such as ileal nutrient digestibility, intestinal histomorphology, and immune function.